Brake slack adjuster



Feb 28, 1956 o. RASMUSSEN ET AL 2,736,396

BRAKE sLAcK ADJUSTER (Ittornegs Feb. 28, 1956 o. RAsMUssl-:N ET AL2,736,395

BRAKE SLACK ADJUSTER Original Filed Nov. 23, 1945 2 Sheets-Sheet 2 Awenfors W aftotnegs United States Patent BRAKE sLAcK ADJUSTER OlafRasmussen, Port Clinton, and Richard C. Rike,

Dayton, Ohio, assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware Original application November 23, 1945, SerialNo. 630,226. Divided and this application June 4, 1951, Serial No.229,836

Claims. (Cl. 18S- 196) This invention relates to improvements in brakesand particularly hydraulically actuated brakes and is `a division of the-applicants copending application Serial No. 630,226, filed November 23,1945, which has matured into Patent No. 2,580,701.

It is among the objects of the present invention to provide an improvedautomatic slack adjuster for a brake.

A further object of the present invention is to provide an improvedslack adjuster for a brake drum having a minimum expansion duringoperation so that temperature compensation mechanism will not benecessary.

In the standard brake, the drum, frictionally engaged by the brakeshoes, becomes heated during braking operations and, due to saidheating, will expand diametrically. Due to this enlargement of the drum,a greater brake shoe travel is required at the higher temperature of thedrum than at the initial, normal temperature, this, therefore, requiresthe brake shoe actuating device to be adjusted to compensate for suchexpansion due to temperature increases in order to maintain thenecessary braking effort.

The brake shoe actuator of the present invention is simplified becauseit need not be adjusted to compensate for expansion of the drum, butonly for brake shoe wear. Simplification of the brake actuating deviceas well as the adjuster is rendered possible under the presentinvention, for the brake drum is of such a size or may be made of such amaterial as to limit its expansion due to temperature rises so as not torequire adjustment for expansion. In the present invention, the brakedrum is of such' a size or is constructed of such a material as to havean expansion which does not exceed the effective operating range ofmovement of the brake shoe actuating device. Thus the normal travel ofthe actuating device is suilcient, in a predetermined range of drumexpansion movements, to move the shoes into braking engagement with thedrum without necessitating adjustment thereof to compensate for suchdrum expansion.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings, wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

Figure 1 is a vertical section through the drum.

Figure 2 is a vertical section of a modification in which the inventionmay be embodied.

Figure 3 is a section on line 3 3 of Figure 2.

The applicants original application Serial No. 630,226, now Patent No.2,580,701, contains a complete description of all the features of thisbrake. Since this application relates to the automatic slack adjuster,the other features are described only in conjunction with thedescription of the slack adjuster. The wheel hub is equipped with a drum23 which is much smaller than the drum usually found on a wheel ofcorresponding size so that a relatively large air space between thewheel rim and the "ice 27 by the interposition of link means 33 pivotednear thev end of the shoe at 35. Diametrically opposite link means 33are other link means 37 which connect an end of shoe 31 to anotheranchor abutment 39.

Because of the relatively small diameter of the drum, it may be extendedmuch more than usual in its axial dimension whereby there is a greaterarea of contact with wider shoes. Also we prefer to apply the brakeshoes by hydraulic applying means and to provide greater effectiveaction than could be provided by a single wheel cylinder within therestricted radial dimension available. Tandem cylinders may be employedas described in the applicants above mentioned application. In thisapplication only the single wheel cylinder 41 at the upper region of theanchor and 45 at the lower region is shown. Within each cylinder is acup-shaped piston 51 having a channeled outer end engaging the roundedend of one of the adjacent brake shoe webs 111. The piston is sealed bypacking 53 and a protecting boot 55 is used between the cylinder and itspiston. In each cylinder there is added a slack adjuster to makecorrection for the released position of the shoes as the lining wears.To that end a slotted disc 57 is staked into the wheel cylinder adjacentits inner end. On the inner wall of the piston or on a sleeve 59 securedtherein are teeth 61. Cooperating with teeth 61 are one or more teeth 63on the arcuate segments of an inner sleeve 65. This last named sleevehas a neck part extending slidably through disc 57 and a head 67 locatedbetween the inner end of the cylinder and the staked disc. Theresiliency of the arms of sleeve 65 holds the teeth in contact with eachother. When the brake is applied the clearance between the head 67 andthe disc 57 permits the sleeve 65 to move outwardly with the piston.Only if more than normal movement of the piston occurs does the tooth orteeth of sleeve 65 engage an adjacent tooth of the piston and determinea new release position. The space through which the head 67 is free tomove accommodates normal shoe clearance and any expansion of the drumdue to heat from friction with the shoes or deflection due to forcesapplied. It will be noted that since the drum is much smaller than usualit is possible to provide a clearance for head 67 which might not bepracticable were the drum of a larger size which would have greaterexpansion or deflection. The number of teeth on the piston sleeve islimited so that after a given extent of slack adjustment is made, nomore adjustment will occur. The operator is thus madeaware of the needfor relining.

Thel pressure fluid is supplied by a master cylinder to a conduit 73,and a connected passage in the anchor to a space 77 at the back of thepistons of the lower pair of wheel cylinders, from which space asuitable conduit 79 conveys it to the space 77 at the back of thepistons associated with the upper cylinders. At the uppermost region ableed passage 81 having a suitable closure permits the removal of thecontents.

The retraction spring mechanism shown in Figure l is completely shownand described in the applicants above mentioned application. To a flange85 integral with the anchor plate 27 is secured a U-shaped member 89.The brake shoe carries a bolt 91 extending radially therefrom and intothe hollow of the member 89 where it has a nut,

93 with two opposed ears 93' (Figure 1) which project through the sideopenings of U-s'naped member 89. Between the ears 93 of the nut and thearch of member 39 is a releasing spring 95. There may be two of theseshoe releasing devices, one for the midportion of each shoe asillustrated. For the details of the lateral positioning means 196mounted on the stamping 97, see the applicants above mentionedapplication.

The brake mechanism thus far described is intended for use as a frontwheel brake. lt will be readily seen that the two shoes areself-energized by drum contact to give self-energized frictionalretarding in one direction only of drum rotation. In checking reversedriving, this type of brake is relatively ineicient since the appliedforce in the case of both shoes acts against the braking forces producedby drum rotation. lt is, however, an arrangement especially eliectivefor checking forward travel and is believed to be desirable for frontwheels. Rearward vehicle movement is slow and it is consideredunnecessary to provide maximum braking on front wheels. This brakeconstruction when employed on vehicies haying standard wheels of or 16inches in diameter will produce the saine retarding force with a brakedrum of not more than seven inches in diameter as the conventional brakewith a drum having a diameter of 1l to 14 inches. With the small brakedrum of seven inches or less in diameter the normal temperature rise ofabout 600 F. will not expand the diameter of the drum more than .035 ofan inch or the circumference more than .110 of an inch. When thisexpansion and distortion of the drum during brake application is reducedto this small value due to the small diameter drum, the lost motion ofthe stem or sleeve 65 mounted on the cylinder as shown in Figure 2 or onthe other piston as shown in Figure 3 may be reduced. Thus the lostmotion of stem 65 is made equal to the movement of the piston normallynecessary to rnove the shoe into braking engagement with the drum at agiven normal operation temperature, and then a distance of not more than.0505 of an inch to maintain said braking engagement for expansion anddistortion of the small drum due to temperature rises during thebraking. With this small seven-inch drum the small expansion does notrequire a noticeable increase in the lost motion required in the slackadjusted above the normal slack employed at constant normal temperaturesto prevent the brake from binding due to the contraction of the drumonto the shoes.

ln the application of this invention to rear wheels there will bedescribed an arrangement wherein self-energization is provided for theshoes in their work of checking rearward as well as forward travelalthough that nicety of drum engagement by the shoes occasioned by thelink anchorage is available only in the act of checking forward travel.It may be added that the arrangement for rear wheels could also beadopted for front wheels if it should be desired. In this second formthe invention has been shown with single cylinders instead of with pairsof cylinders, it being believed that in many installations it will beentirely possible to apply the shoes without the duplication of wheelcylinders described above.

Considering then, Figures 2 and 3, numeral 151 is used to designate theshoe torque taking anchor. It is rigid with the axle housing as usual.The small brake drum 153 is carried by the wheel in any convenient way.The anchor closes the open end of the drum and has an annular partprojecting over the axle bearing and into the hollow drum. Radiallyenlarged parts 159 are formed with cylinders 161 open at both endswithin which are pistons 163 and 165 (Figure 3). Each anchor enlargementcarries pins 161i on each side of the cylinder for the support of links167 connected to the ends of one of the shoes. Intermediatereinforcements 169 at both ends of both Cyl shoes are engaged by therecessed ends of the pistons. One of the pistons of each pair isassociated with a slack adjuster which, except for its supporting meansin the other piston, is like that of the Figure 2. The provision forbrake release and for holding the shoe away from the drum is like thatshown by Figure l and need not be again described. At the link ends ofthe shoes are bolts or pins 171 carried in this case by shoe webs 173and by reinforcement 169. A suitable conduit from the master cylinder isconnected in any convenient manner to the space between the pistons ofthe lower wheel cylinder and the upper cylinder derives its source oftluid from a pipe 175 leading from the lower cylinder.

With this arrangement, forward vehicle travel is to be understood ascausing clockwise rotation of the drum shown in Figure 2. The lower leftpiston applies the left shoe which anchors by means of its link 167. Atthe same time the upper right piston applies the right shoe anchoring bymeans of its links. The nice lit with the drum because of the links andself-energization caused by drum rotation supplementing the appliedforce makes this a very etective brake. For reverse travel the rightlower piston pushes the righ shoe, the adjacent link leaving its anchorpin and similarly the left upper piston applies the left shoe. The drumrotation thus aids the hydraulic application for checking reverse aswell as forward travel. It will be seen that a shoulder 171 on thepiston anchors on the cylinder end in the case of reverse travel.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

We claim:

l. A slack adjuster for hydraulic brakes including a wheel cylinder, ahollow piston within said cylinder, a limited number of teeth projectinginwardly within said piston, a tubular adjusting pin having a slottedwall and a head, means in the cylinder to provide limited free movementfor said head, said slotted wall having one or more formations extendingoutwardly to engage said piston teeth to determine progressive positionsof brake release to correspond with lining wear.

2. The invention defined by claim l, said limited number of teeth onsaid piston limiting extension of said wheel cylinder and terminatingautomatic adjustment before the shoe lining is fully worn.

3. The invention deiined by claim l, said cylinder having a secondopposed piston and said means to afford limited free movement for saidpin head being in said second piston.

4. A slack adjuster for hydraulic brakes including a wheel cylinderhaving an end wall and a shoulder adjacent said end wall, a hollowpiston within said cylinder having an inner wall, a limited number ofteeth projecting from said inner wall of said hollow piston, anadjusting member positioned within said hollow piston, said adjustingmember having a head at one end located between said end wall and saidshoulder and having limited movement, and said adjusting member havingone or more formations to engage said piston teeth to determineprogressive positions of brake release to correspond with lining wear.

5. In a slack adjuster for hydraulic brakes, a wheel cylinder includinga member and a piston having an interna] cavity at one end with aninternal wall, said piston being movable relative to said member by uidpressure contacting said one end and entering said cavity, ratchet teethon said internal wall projecting inwardly within said hollow piston, atubular adjusting pin having a slotted resilient wall extending over aportion of the tube adjacent yone end positioned within said hollowpiswv esta ton, said slotted wall having a projection adjacent said oneend to engage said ratchet teeth to permit relative movement of saidmember and piston in one direction and to prevent relative movement inthe other direction, and means engaging the other end of said tubularadjusting pin to mount the pin on said member for limited free axialmovement.

References Cited in the file of this patent UNITED STATES PATENTS1,668,730 Pearson May 8, 1928 5 2,404,326 Taylor July 16, 1946 j FOREIGNPATENTS 730,210 France May 9, 1932

